Wireless communication systems are advancing to provide good service quality, support a high data rate and keep up with the continuously increasing demand for wireless data traffic.
Traditionally, reference signals (RSs) are used to determine service quality of cells. By way of example, Channel State Information Reference Signal (CSI-RS) or Demodulation Reference Signal (DMRS) may be transmitted from multiple cells to mobile terminals. By means of measuring CSI-RS or DMRS from neighboring cells, a mobile terminal can know cell quality of its serving cell and neighboring cells and then report back to a base station serving the mobile terminal, so that the base station determines which cell the mobile terminal should connect to.
In recent wireless communication systems, a cell is provided by a beam of a base station, and a base station has a plurality of beams and thus provides multiple cells. As to a beam provided by a base station, there may be neighboring beams, including beams (also referred to as “local beams” hereafter) provided by the same base station and beams (also referred to as “neighbor beams” hereafter) provided by neighbor base stations.
For purpose of reducing interferences generated by the RSs which are always on, mobility reference signals (MRSs) have been proposed to be transmitted on demand. In this case, the mobile terminal and/or the base station do not know the neighboring beam quality until the MRSs are activated and transmitted. There are generally two modes to trigger the MRSs, namely an intra-node beam switch mode and an inter-node beam switch mode. In the intra-node beam switch mode, if quality of a serving beam is low, MRSs will be triggered to be transmitted from the local beams. In inter-node beam switch mode, if quality of a serving beam is low, MRSs will be triggered to be transmitted from the neighbor beams.
Conventionally, in the case that the quality of the serving beam is low, both the inter-node beam switch mode and the intra-node beam switch mode are triggered. As such, MRSs will be triggered to be transmitted from both the local beams and neighbor beams to the mobile terminal, and the mobile terminal has to measure all the received MRSs. Since there is no differentiation between the intra-node beam switch and the inter-node beam switch mode, an undesirable signaling overhead and work load issue would occur and needs to be mitigated.